Process of making color-printing plates



Patented Nov. 8, 1932 1 menses JOHN Ml REE-NAN, E TORONTO, ONTARIO;CANADA 'IPROCESS OF MAKING COLOR-PRINTING PLATES Ho Drawing.

This invention relates to the production of the half tone plates used ininulti-color lithographing and printing processes. Urdinarily the platesare prepared from negatives 5 taken by photographing the colored subjectfirst through'a green filter, then through a red filter and then througha blue filter, and, in four color works, through a pale amber filter toproduce the black plate. Thus color separations are obtained, that isnegatives, one of which is supposed to represent all the yellow in thesubject, another all thered and another all the blue, While the black,"plate represents the Whole of the tones of the original in their properrelation to each other.

Unfortunately, however, it is mainly supposition, as light filters WhichWill'pass the rudimentary printing colors in theirproper proportions areunattainable. 2G The result is that, when the plates produced from thesecolor-separation negatives are prepared, a great deal of hand W0; isrequired to make each plate represent as truly as possible the values ofthe color which it represents. i

ln the case of photo-engraving this work comprises stopping out orstaging parts of the plate which are suficiently etched and re-etchingby hand those parts insufificiently etched to loring out the propervalue of the color. This Work is done in stages until finished andafterwards proofs must be pulled, with all three or four impressionsproperly superimposed, in order to determine how accurately the colorsof the original are produced. If the results are not satisfactory thisgoes on till the plates are satisfactory. This hand Work takes a lot ofthe time of shill-ed and highly paid labor. For instance, fromforty-five to sixty hours of time is average for an ordinary job,

My object in the present invention is to obtain proper values the colorsthe printing plates as ar as possible by photomechanical means, oughsome small amount of hand Work may in some oases he necessary -for thefinest results, thus eliminating nearly all the hand staging andre-etching non required on the printing plates themselves. 0 This is efiecteol in the following manner. lt

'colorfilter lets through some redand some Application filed March 26,1931, "Serial No. 525,609.

appears that thegreen color filter lets through some blue light, thatthe red color filter also lets througl'r some blue light, that the blueyellow light, and that the blaclr negative, though taken through a paleamber filter does not give the tonal values of the original exactlyenough. Therefore, to obtain sub-- stantially correct color values inthe final positives, which are used as copy for the making of the colorplates, or transparencies for i use in the production of the replicas ofthe original copy, some means must be provided to cut-out the effects orthe intrusive color When preparing a positive from a colorseparationnegative This is done by superimposing on the color-separation negative(yellow, red, or blue, as the case may be) a positive, or cut out takenfrom the complem ntary color separation negative and then, by means ofthe camera, making a positive lay means oi light transmitted through thecombination K This complementary positive or out-out usually remains inposition during part only of the time oi exposure and then exposure iscompleted with light transmitted by the color separation negative only.As the complementary positive or cut-out represents color valuescomplementary to those of the color-separation negative, it cuts downthe ellect oi the transparency of the colorseparation negative, Wherethe complementary color has affected it, so that the positive printedfrom the combination has cut out of it the eilect of the passage of thecomplementary color which passes the filter and afiected theoriginal.color-separation negative. In practice employ a cut-outrepresenting blue with a yellow color-separation negative, a cut-outrepresenting blue with color-separation negative, and emloy with a loluecolor-separation negative, st a cut-out representing red, and then,reierably, a cut-out representing yellow each for part of the time ofexposure), and v ith the blacl? negative all three cut-outs ueoessively(each for part of the time of exosure}, f

the ease of the making of the positives in'rti from the blue and theblack color-separation negative the exposure may also be for part timewithout using a cut-out.

The color separation negatives and positives are, of course, appliedface to face so that the films are in substantially the same focalplane.

With the'method of overlaying the colorseparation negatives with cut-outpositives, made from complementary color-separation negatives, any tonalefi'ects desired may be produced, as the cut-out efiect is readilyvaried by varying the ratio of the time exposure of the final positive,with a cutout in position, to the total exposure.

This process demands perfect registration of a color-separationnegative, and the cut-out employed and any known apparatus may beemployed for this purpose.

The final positives are used in any known manner to produce the printingplates used in makin replicas of the original copy.

What claim as my invention is:

1. In a process of making color-printing plates the steps which consistin making ordinary color-separation negatives from an originalrepresenting the three primary printing colors red, yellow and blue;making positives from said negatives; superimposing a positive takenfrom the blue color separation negative on the yellow color separationnegative to serve as a corrective cut-out; superimposing a positivetaken from the blue color separation negative on the yellowcolor-separation negative to serve as a corrective cut-out);superimposing on a blue colorseparation negative a positive taken from acolor-separation negative representing light of a longer wave length;and, with a camera, producing a positive of each combination by lighttransmitted therethroug'h.

2. In a process of making color rinting plates the steps which consistin making ordinary color-separation negatives from an originalrepresenting the three primary printing colors red, yellow and blue;making positives from said'negatives; superimposing a positive takenfrom the blue color-separation negative on the yellow color-separationnegative to serve as a corrective cut-out; superimposing a positivetaken from the blue color-separation negative on the yellowcolorseparation negative to serve as a corrective cut-out; superimposingon ablue colorseparation negative first a positive taken from the yellowcolor-separation negative and subsequently, after removingthe saidpositive, a positive taken from the red colorseparation negative; and,with a camera, producing positives from the combinations by lighttransmitted therethrough, the exposure in the case of the bluecolor-separation negative being for part time with the yellow cut-out?in place and part time with the red cut-out in place 3. A process ofmaking color printing plates as set forth in claim 2 in which the finalpositive taken from each color-separation negative is exposed for parttime without a cut-out positive superimposed.

4. In a process of making color-printing plates the steps which consistin making ordinary color-separation negativesv from an originalrepresenting the three primary printing colors red, yellow and blue andalso a so-called black negative; making positives from eachcolor-separation negative -to serve as a corrective cut-out; makingfinal positives from the three color-separation negatives and from theblack negative, with a camera by transmitted light; and using saidcut-out positives to-correct the color values in the last-mentionedpositives by super-imposition on the negatives during exposure.

5. A process according to claim 4 in which the exposure of the finalpositives is made for part time with the use of the Fcut-out positivesand part time without.

6. A process according to claim 4 in which the final positives made fromthe blue colorseparation negative and the black negative are made, usingboth the yellow and red cutout positives in the case of the bluecolorseparation negative and 'all three cut-out positives in the case ofthe black negative.

- 7. A process according to claim 4 in which the final positives madefrom the blue colorseparation negative and the black negative are made,using both the yellow and red cut-out positives in the case of the bluecolor-separation negative and all three cut-out positives in the case ofthe black negative and in which the exposure of the final postives ismade for part time with the use of the cut-out without.

positives and part time Signed at Toronto, Canada, this 19th day I ofJanuary, 1931.

. JOHN M. KEENAN.

